Pediculosis (lice infestation) in humans has been known since ancient times. Lice infestations are common throughout the world. In the United States alone, an estimated ten million cases of pediculosis occurred during 1985 and the numbers have increased substantially since then. In Europe, lice infestation has reached epidemic proportions.
Three types of lice infest humans: 1) head lice, 2) body lice and 3) crab or pubic lice. All are members of the family Pediculidae and most are species within the genus Pediculus. They are small, flat, grayish-black, wingless insects. Their six legs are short and stout, with a large claw on each leg for grasping and holding onto hair. They have piercing and sucking mouth parts for blood feeding and require close contact with human hosts, to which they are very well adapted. The three types differ considerably in habitat and to a small degree, in their life cycles. Lice also infest domestic, farm and wild animals.
Acarine arachnids, or mites, have a serious effect upon man and his environment. House dust mites are the main causative agent of exacerbations of one of the worst ailments of twentieth-century man--asthma. Mites and ticks can carry serious pathogens which threaten man and cause morbidity in livestock. Psoroptid mites produce mange in both farm and domestic animals and sarcoptid mites cause much suffering and discomfort through scabies. Mites also infest many crop plants.
Other insects, whether directly parasitic upon man and his animals or by virtue of infesting the human environment in large numbers, can cause much hardship and destruction. Amongst many species which cause such problems are ants.
Terpenes are bio-active compounds and there are numerous reports in the literature concerning their effects as antibacterial, antifungal, antihelminthic and antimitotic agents. Various terpenes are used in agriculture for growth inhibition, growth promotion and in the food industry as flavorings and fragrances. Interest in the potential for using terpenes in medical applications is increasing.
Citral is a component of certain essential oils, in particular lemongrass (Cymbopogon citratus), and is typically produced by steam distillation. It can also be produced synthetically. It is a terpene aldehyde with the molecular formula C.sub.10 H.sub.16 O and has a molecular weight of 155.24. It is known to have limited antibacterial and anti-fungal effects.